1. Field of the Invention
This invention relates to a filtration cartridge for a gravity-flow water system. More specifically, this invention relates to a gravity-flow filtration cartridge for use in a home, office and outdoors that features a complex, tortuous path matrix which removes microorganisms, such as Cryptosporidium and Giardia lamblia, in addition to removing heavy metals, chlorine, taste and odor from water.
2. Description of the State of Art
Water quality in industrialized nations has recently become a major concern for many people primarily because of health concerns due to trace quantities of heavy metals, such as lead, copper and zinc, but also in-part because of odors and the taste of chlorine in water. While legislation in the United States has eliminated, from new construction, materials that leach lead and other heavy metals into water, the early nineties saw the discovery that chlorine-based chemicals, used to treat America""s water supplies, may also pose serious health risks. In 1995 the non-profit National Resources Defense Council found that there may be as many as 7 million cases of drinking water-related illnesses each year in the United States, with about 1,200 deaths. In 1993 and 1994 alone, roughly 53 million Americans, one in five, drew their drinking water from systems that violated Environmental Protection Agency regulations. Chlorine in tap water has been reported to be linked to chemical bi-products, called trihalomethanes (THMs) that have proven to be carcinogenic when consumed over long periods of time. Trihalomethanes are now directly linked to colon and bladder cancer in humans. Another report by Dr. Charles Gerba concludes that 39% of municipally treated tap water is contaminated with either Giardia lamblia or Cryptosporidium, or both. Cryptosporidium, a pathogenic protozoan microorganism, was responsible for outbreaks in Milwaukee and Las Vegas in the early 1990s. In the Milwaukee outbreak of Cryptosporidiosis, 400,000 people were sickened, as many as 4,000 people were hospitalized, while over 100 people died as a direct result of drinking microbiologically contaminated tap water. These discoveries, combined with growing public acceptance of bottled water and water filtration systems, have caused tremendous growth in the sale of both bottled water and the further development of water filters for the home, office, and outdoors. Today, a growing number of people choose to use bottled water or use a water filtration device to filter their drinking and/or cooking water.
Several types of gravity-flow filtration systems have been developed to address the various health concerns addressed above. The most popular styles being the pour-through carafe or the refrigerator water tank, which have been developed by such companies as Clorox""s(trademark) BRITA(trademark), Recovery Engineering""s PUR(trademark), Water by Culligan(trademark), Rubbermaid(trademark) and Glacier Pure(trademark). Such systems include an upper reservoir for receiving unfiltered water, a lower reservoir for receiving and storing filtered water, and a granular activated carbon filter with an inlet at its top and outlet at its bottom which allows water to flow from the upper reservoir to the lower reservoir. The pour-through carafe is sized to be handheld, holds about two liters of water, and may be tipped for pouring filtered water, as in a conventional pitcher or carafe. The refrigerator tank system is typically a larger rectangular tank with a spigot for draining filtered water into a glass or pan. Both the carafe or tank designs use gravity to cause the unfiltered water in the top reservoir to flow down through the filter cartridge and into the lower reservoir where the filtered water remains until it is used.
The gravity-flow filtering devices, herein also referred to as xe2x80x9cpour-throughxe2x80x9d devices, originated in Europe. Their development was partly due to there being no standard pipe thread size in Europe, making a faucet-connected filter impractical and inoperable in most cases. Introduced into Canada and then the United States in 1987, the pour-through devices have become popular in the United States because of their economy, ease of use, portability, and because they require no plumbing or other installation. The pour-through devices store easily in the refrigerator, providing accessible chilled drinking water, and they are inexpensive, which accommodates first time buyers who are trying out such devices.
The traditional filter cartridge used in pour-through devices holds a granular blended media of 20xc3x9750 mesh granular activated carbon and either an ion exchange resin most typically a weak acid cation exchange resin or a natural or artificial zeolite which facilitates the removal of certain heavy metals such as lead and copper from tap water. While weak acid cation exchange resins also reduce hardness slightly, some disadvantages are also associated: first, they require a long contact time to work properly, which limits the flow rate to about one-half liter per minute; second, they take up a large amount of space inside the filter, or about 65% of the total cubic volume, thus limiting the space available for activated carbon. For these reasons exchange resins have never been used effectively in any configuration other than a gravity flow device.
Alternate forms of lead removal are through the use of natural and artificial zeolites, commonly called sorbents. Zeolites are a natural hydrated silicate of aluminum and either sodium or calcium or both. Natural zeolites are analcite, chabazite, heulandite, natrolite, stilbite and thomsonite. Zeolites can also be produced artificially. These are made in a variety of forms ranging from gelatinous to porous and sand-like, and are used as adsorbents, drying agents and catalysts as well as water softeners. Engelhard manufactures an artificial zeolite using titanium, in which the aluminum is replaced by the titanium under a proprietary process. This sorbent is marketed as ATS(trademark) and ATC(trademark). Selecto Scientific also produces an activated alumina zeolite, which is marketed under the brand name Alusil. These sorbents remove heavy metals more quickly and have the advantage of taking up far less space, typically 10% to 20% of the filter volume. However, they are only rarely used in loose granular media water filters since at pH levels of 9.5 and greater they have been known to precipitate any lead they have adsorbed back into the water. This problem can be remedied, however, when used in combination with a solid carbon block or other barrier that is positioned downstream of the sorbent. As lead leaches back into the water in precipitate form, the solid carbon block physically captures the lead and will not allow it to flow through the filter device.
Another problem with lead sorbents in powdered or granular form is that they will segregate from granular activated carbon when used in loose form. This in turn cretes the potential for channeling, a process by which water channels through only a portion of the media and is never 100% exposed to all of it. The activated carbon removes most of the chlorine from ordinary tap water, thereby improving its taste, color and odor. While activated carbon will further remove organic content from water, this is typically unnecessary since chlorinated tap water is generally free of organic matter, which is oxidized off in the chlorination process. While some trihalomethanes (THMs) still show up in treated water, trihalomethanes are now strictly regulated by the EPA and are limited to permissible levels. Further, many municipalities are now using chloramines instead of free chlorine. Chloramines are known to be more stable as a disinfectant and will not produce trihalomethanes when combined with organic matter.
Although these pour-through devices have been quite effective in reducing lead to under 15 parts per billion (ppb), as well as reducing chlorine by 75% to 95%, thereby improving the taste, color and odor of tap water, most pour-through devices have not been effective in removing water-borne microorganisms such as Cryptosporidium and Giardia lamblia. One exception is the PUR(trademark) Plus carafe, which does effectively eliminate Cryptosporidium as well as chlorine and lead. This method employs a pleated, hydrophilic membrane, through which water flows radially; then the water drips through a blended media for removal of other contaminants. This method is expensive, nearly doubling the cost to the consumer; and it is vulnerable to turbidity in water in which case the microscopic pores (under 3 microns absolute) can clog prematurely.
Therefore, there is a need for a gravity-flow filtration system for use in the home, office, and outdoors that can remove microorganisms as well as chlorine, and heavy metals out of tap water, well water, and lakes and streams; yet be cost effective so that most consumers can safely filter water from the tap.
Accordingly, it is a general object of this invention to provide a convenient gravity-flow xe2x80x9cpour-throughxe2x80x9d water filtration device for municipally treated tap water as well as for water from lakes and streams, which can remove microorganisms, and specifically water-borne parasites such as Cryptosporidium and Giardia lamblia. 
Another object of the invention is to provide a gravity-flow filtration device to further remove chlorine, heavy metals, taste, color and odor from water.
Additional objects, advantages and novel features of this invention shall be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following specification or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities, combinations, compositions, and methods particularly pointed out in the appended claims.
To achieve the foregoing and other objects and in accordance with the purposes of the present invention, as embodied and broadly described therein, the apparatus of this invention may comprise a filtration cartridge which houses a liquid porous plastic element having an inlet side and outlet side, and pores with a mean pore diameter in the range of 10-20 microns.